Study and fabrication of buried oxide layers in GaAs/AlAs structures for confinement engineering in photonic devices

摘要

The thermal oxidation of an Al-rich AlGaAs buried layer is a common established technique used to improve the performances of some optoelectronic devices, like VCSEL or optical waveguides, in terms of electro-optical confinement. This oxidation technique is usually proceeding laterally, which allows achieving good results but leads to some difficulties on the control of the shape and size of the oxidized areas. In this work, a new technology to oxidize GaAs/AlAs epitaxial structures which avoids these limitations is presented. This method consists of an oxidation through the top of the sample, allowing in consequence a total control of the shape of oxidation by means of photolithography. For this purpose the method has two steps: first, the intentional creation of defects in the top GaAs layer, in order to make it possible the oxidant species diffusion through this material, and second the planar oxidation of the AlAs layer. In this paper this technique is thoroughly studied: different methods to create defects in the GaAs layer have been analysed, and the optimization of the procedure has been achieved leading to a uniform oxidation and a reduced lateral oxidation spreading. Finally a comparison between the experiments and simulations has been realized in order to provide an explanation for this type of vertical oxidation. This innovating technique allows addressing separately the electrical and optical operating aspects of optoelectronic devices, thus opens to novel structures with controlled transverse optical behaviour.